Thermal strain is a leading cause of discomfort in clothing. Different materials provide different thermal comfort characteristics for a wearer of the materials in a particular environment. Further, changes in material properties result in discernible differences to the wearer. Typically, an actual product use test is required to determine whether a particular change to one of the material properties results in a meaningful difference to the wearer.
Some existing systems attempt to model human thermal comfort. These existing models, however, are limited to a single garment on a human subject or fail to account for various factors such as environmental conditions (e.g., work conditions), garment use scenarios, or physiological data for the specific human subject evaluating the garment. Methods exist that attempt to describe the thermal strain of a human, clothing, environment system. This type of model places emphasis on describing the physiological changes to the subject and characterizes clothing ensembles and fabric layers as a single barrier to heat and moisture movement. This ignores the significance of fabric and air layers as places where heat and moisture may be stored or produced. Other models focus on characterizing heat and moisture movement in fabric layer systems but simplify or ignore the interaction with the subject.
Existing software packages incorporate subject physical properties, their activity level, environmental conditions and clothing characteristics. While these types of models provide insight into thermal stress and thermal comfort for particular clothing ensembles, these existing models do not provide for the calculation of the moisture and thermal insulation properties of these ensembles nor do they account for the dynamics of the fabric properties such as heat of sorption. Additionally they ignore the thermal and moisture capacity of the fabric and air layers and are generally designed only for determining long-term, steady state conditions. Further, the existing models fail to consider the dynamics of the clothing ensemble during usage conditions that are relatively short in duration.